A mixture of dimethyl 4-acetamido-5-nitrophthalate, methanol and 5% platinum on carbon is hydrogenated in a Parr hydrogenator. The reaction mixture is filtered through diatomaceous earth and the filtrate is concentrated in vacuo. The thus-obtained crude diamine intermediate (48.09, 0.180 mol) is mixed with p-toluenesulfonic acid (51.4 g, 0.270 mol) and toluene (400 mL), and stirred for 2 hours at reflux temperatures with azeotropic removal of water, cooled and concentrated in vacuo. The resultant residue is recrystallized from methanol to afford the p-toluene sulfonate salt of the title product. The salt is dissolved in hot water, made basic with sodium bicarbonate and extracted with methylene chloride. The combined extracts are washed with brine, dried (MgSO4) and concentrated in vacuo to give a red solid. Recrystallization of a portion of the red solid affords the title product as white crystals, mp 151°-152° C.
